JP2023068531A - Insulation type dc/dc conversion device, control method therefor, and power conversion system - Google Patents

Abstract

To control a voltage of a smoothing capacitor within a predetermined operation time and in a relatively short time in a simplified configuration in relative to the prior arts in a preparing action prior to operation of an insulation type DC/DC conversion device.SOLUTION: An insulation type DC/DC conversion device comprises: a first smoothing unit including a capacitor for smoothing an input voltage; a switching unit consisting of a transformer for insulation, an inductor, a primary-side switching circuit of the transformer for insulation and a secondary-side switching circuit of the transformer for insulation, the switching unit being configured to switch the smoothed voltage and perform power conversion into a predetermined output voltage; a second smoothing unit including a capacitor for smoothing the power-converted output voltage; and a control unit for controlling a preparing action before starting operating the switching unit. In the preparing action prior to the operation start, the control unit controls the switching unit to regulate the input voltage and the output voltage in such a manner that an inductor current flowing in the inductor becomes less than an upper limit value based on the input voltage and the output voltage.SELECTED DRAWING: Figure 12

Description

The present invention relates to an insulated DCDC converter, its control method, and a power conversion system.

A conventional insulated DCDC converter is configured with switching circuits each comprising a plurality of switches on both sides of a transformer for electrical isolation, and smoothing capacitors on the outsides of the switching circuits. If there is a potential difference between the pair of smoothing capacitors, there is a problem that a large current flows during operation of the DCDC conversion device, and the parts are destroyed. In order to solve this problem, it is necessary to adjust the voltage of the pair of smoothing capacitors as an operation before starting operation. Decrease the voltage on the capacitor. Also, during charging, it is connected to a charge consumption resistor through a switch in order to prevent an inrush current.

For example, Patent Literature 1 discloses a power conversion device and a control method that can start operation without generating an excessive current in components that make up a DC/DC converter even when there is a voltage difference between two capacitors. . This power conversion device includes an insulated DC/DC converter that converts one DC power through AC power into the other DC power, and the insulated DC/DC converter is a first conductor of one DC power. A first capacitor connected to the path, a second capacitor connected to the other DC power second conduction path, and a first current limiter for suppressing current flowing in the AC power third conduction path. circuit. Specifically, in the power conversion device of Patent Document 1, when there is a potential difference between the input smoothing section and the output smoothing section as a preliminary charge before starting operation, the switch of the current limiting circuit is turned off, and current flows through the current limiter. , controlling the current to be limited.

Further, in Patent Document 2, in an insulated DC/DC converter, insulation for safely charging the voltage of a capacitor while suppressing inrush current during precharging without providing a current detection sensor or an overcurrent prevention circuit A control circuit for a type DC/DC converter is disclosed. The control circuit of this isolated DC/DC converter performs voltage control according to the deviation between the first capacitor voltage and the second capacitor voltage. Then, based on the result of the voltage control, it generates gate signals for a plurality of semiconductor switch elements provided in the insulated DC/DC converter. Specifically, the control circuit of the isolated DC/DC converter of Patent Document 2 performs voltage control according to the voltage deviation between the input smoothing section and the output smoothing section as preliminary charging before starting operation, and determines the phase difference. A plurality of semiconductor switch elements are controlled so that overcurrent does not flow.

JP 2017-118806 A JP 2021-078274 A

However, in the conventional insulated DCDC converter, it is necessary to provide a charge consuming resistor and a switch, which increases the size of the circuit and increases the cost of the circuit.

Further, in the power conversion device of Patent Document 1, it is necessary to provide a current limiting circuit, which causes the problem that the size of the circuit increases and the cost of the circuit increases.

Furthermore, in the control circuit of the isolated DC/DC converter of Patent Document 2, the control sequence of the control circuit becomes complicated, and there is a problem that the processing time becomes long when the control circuit is implemented in a microcomputer or the like.

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems, and in the preparatory operation before operation of an insulated DCDC converter, the structure is simpler than that of the prior art, and smoothing is achieved within a predetermined operation time in a relatively short time. An object of the present invention is to provide an insulated DCDC converter capable of controlling the voltage of a capacitor, a control method thereof, and a power conversion system.

An insulated DCDC converter according to one aspect of the present invention comprises:
a first smoothing unit including a first capacitor for smoothing an input voltage;
A switching unit composed of an insulating transformer, an inductor, a switching circuit on the primary side of the insulating transformer, and a switching circuit on the secondary side of the insulating transformer, and switches the smoothed voltage. a switching unit that converts power to a predetermined output voltage;
a second smoothing unit including a second capacitor for smoothing the power-converted output voltage;
An insulated DCDC converter comprising a control unit that controls a preparatory operation before starting operation of the switching unit,
The control unit adjusts the input voltage and the output voltage based on the input voltage and the output voltage in a preparatory operation before starting operation so that an inductor current flowing through the inductor is less than a predetermined upper limit value. The switching unit is controlled so as to

Therefore, according to the insulated DCDC converter and the like according to one aspect of the present invention, in the preparatory operation before operation of the insulated DCDC converter, the configuration is simpler than that of the conventional technology, and the comparison can be made within a predetermined operation time. It is possible to control the voltage of the smoothing capacitor in a relatively short time.

1 is a block diagram showing a configuration example of a power conversion system according to an embodiment; FIG. 2 is a circuit diagram showing a configuration example of an insulated DCDC converter 2 of FIG. 1; FIG. FIG. 3 is a flow chart showing preparatory processing performed by the control unit 10 of FIG. 2 before operation is started; FIG. 3 is a timing chart of each signal showing an operation example when the inductor current IL is continuous in step-up switching and synchronous rectification is performed in the isolated DCDC converter 2 of FIG. 2; 3 is a timing chart of each signal showing an operation example when inductor current IL is continuous in step-up switching and synchronous rectification is not performed in the isolated DCDC converter 2 of FIG. 2; 3 is a timing chart of each signal showing an operation example when the inductor current IL is discontinuous in step-up switching and synchronous rectification is performed in the isolated DCDC converter 2 of FIG. 2. FIG. 3 is a timing chart of each signal showing an operation example when the inductor current IL is discontinuous in step-up switching and there is no synchronous rectification in the isolated DCDC converter 2 of FIG. 2; 3 is a timing chart of the inductor current IL when the inductor current IL is at the maximum value in step-up switching and the inductor current IL is continuous in the isolated DCDC converter 2 of FIG. 2; 3 is a timing chart of the inductor current IL when the inductor current IL is at the maximum value in step-up switching and the inductor current IL is discontinuous in the isolated DCDC converter 2 of FIG. 2; 3 is a timing chart of each signal showing an operation example when inductor current IL is continuous in step-down switching and synchronous rectification is performed in the isolated DCDC converter 2 of FIG. 2; 3 is a timing chart of each signal showing an operation example when the inductor current IL is continuous in step-down switching and without synchronous rectification in the isolated DCDC converter 2 of FIG. 2; FIG. 3 is a timing chart of each signal showing an operation example when the inductor current IL is discontinuous in step-down switching and synchronous rectification is performed in the isolated DCDC converter 2 of FIG. 2 ; FIG. 3 is a timing chart of each signal showing an operation example when the inductor current IL is discontinuous in step-down switching and there is no synchronous rectification in the isolated DCDC converter 2 of FIG. 2; 3 is a timing chart of the inductor current IL when the inductor current IL is at the maximum value in step-down switching and the inductor current IL is continuous in the isolated DCDC converter 2 of FIG. 2; 3 is a timing chart of the inductor current IL when the inductor current IL is at the maximum value in step-down switching and the inductor current IL is discontinuous in the isolated DCDC converter 2 of FIG. 2; FIG. 3 is a flow chart showing a pre-charging control process (outline control flow) executed by control unit 10 in FIG. 2 ; FIG. 3 is a diagram showing a table of charge/discharge control modes executed by a switching unit 9 of FIG. 2; FIG. FIG. 3 is a flowchart showing a first part of a pre-charging control process (detailed control flow) executed by control unit 10 of FIG. 2; FIG. FIG. 3 is a flowchart showing a second part of a pre-charge control process (detailed control flow) executed by control unit 10 of FIG. 2; FIG. 3 is a flowchart showing a third part of a pre-charging control process (detailed control flow) executed by control unit 10 of FIG. 2; It is a simulation result of the insulation type DCDC converter 2 of FIG. 2, Comprising: It is a timing chart of each signal. It is a block diagram which shows the structural example of the power conversion system which concerns on a modification.

Hereinafter, embodiments and modifications according to the present invention will be described with reference to the drawings. In addition, the same code|symbol is attached|subjected about the same or similar component.

(embodiment)
FIG. 1 is a block diagram showing a configuration example of a power conversion system according to an embodiment. In FIG. 1, the power conversion system according to the embodiment includes, for example, a storage battery 1 mounted on an electric vehicle (EV), and an insulated DCDC that has an isolation transformer and converts the DC voltage from the storage battery 1 into a predetermined DC voltage. It comprises a conversion device 2 and a DCAC inverter device 3 that converts a DC voltage from the insulated DCDC conversion device 2 into an AC voltage by switching and outputs the AC voltage to a load of the electric power system or the load 4 . Here, the power system or the load 4 becomes the power system 4 during interconnected operation, and becomes the load 4 during isolated operation.

In FIG. 1, when the storage battery 1 is discharged, the insulated DCDC converter 2 converts the DC voltage output from the storage battery 1 into an AC voltage, and then ACDC-converts the AC voltage into a DC voltage for output. It constitutes a pressure converter device. The DCAC inverter device 3 converts a DC voltage into an AC voltage and outputs it to the power system 4 during grid-connected operation and to the load 4 during isolated operation.

FIG. 2 is a circuit diagram showing a configuration example of the insulated DCDC converter 2 of FIG. In FIG. 2, the insulated DCDC converter 2 has, between each pair of terminals T11, T12; T13, T14,
(1) switches SW1 and SW2 controlled by the control unit 10;
(2) a voltage detection unit 11 that detects a voltage V1 between the terminals T11 and T12 and outputs the detected voltage V1 to the control unit 10;
(3) a smoothing capacitor C1 as a first smoothing unit;
(4) a switching unit 9 including switching circuits 7 and 8, an inductor L, an insulating transformer TR having a primary winding L1 and a secondary winding L2, and a current detection unit 13;
(5) a smoothing capacitor C2 as a second smoothing unit;
(6) a voltage detection unit 12 that detects the voltage V2 between the terminals T13 and T14 and outputs the detected voltage V2 to the control unit 10;
configured with

Here, the terminal T11 is connected to one end of the voltage detection section 11, one end of the smoothing capacitor C1 and one end of the switching circuit 7 via the switch SW1, and the terminal T12 is connected to the other end of the voltage detection section 11 via the switch SW2. , to the other end of the smoothing capacitor C1 and the other end of the switching circuit 7 . A terminal T13 is connected to one end of the voltage detection section 12, one end of the smoothing capacitor C2 and one end of the switching circuit 8, and a terminal T14 is connected to the other end of the voltage detection section 12, the other end of the smoothing capacitor C2 and the switching circuit 8. connected to the end.

The switching circuit 7 includes reverse conduction diodes D1 to D4 connected in parallel and connected in a bridge configuration, and includes four switching elements Q1 to Q4 made of, for example, MOSFETs. 10 to output an AC voltage by switching according to the gate control signals Sg1 to Sg4 which are PWM signals from 10 . In addition, the switching circuit 8 includes four switching elements Q5 to Q8, each of which is connected in parallel with diodes D5 to D8 for reverse conduction and connected in a bridge configuration, and which is formed of, for example, a MOSFET. It switches according to the gate control signals Sg5 to Sg8, which are PWM signals from the control section 10, and outputs an AC voltage.

A connection point between the source of the switching element Q1 of the switching circuit 7 and the drain of the switching element Q3 is connected to the source of the switching element Q2 of the switching circuit 7 via the current detection unit 13, the inductor L, and the primary winding L1 of the transformer TR. It is connected to the connection point with the drain of the switching element Q4. A connection point between the source of the switching element Q5 and the drain of the switching element Q7 of the switching circuit 8 is connected to the source of the switching element Q6 of the switching circuit 8 and the drain of the switching element Q8 via the secondary winding L2 of the transformer TR. connected to the connection point of

In the isolated DCDC converter 2 configured as described above, the DC voltage output from the storage battery 1 is supplied to the switching unit 9 via the terminals T11 and T12, the switches SW1 and SW2, the voltage detection unit 11 and the smoothing capacitor C1. is entered. The switching unit 9 is controlled by the control unit 10, converts an input DC voltage into an AC voltage, and then converts the converted AC voltage into a DC voltage. output through Here, the switches SW1 and SW2 are turned on when the storage battery 1 is charged or discharged, and turned off when not in operation. The smoothing capacitors C1 and C2 each smooth the input DC voltage so as to minimize ripple and output the voltage. The smoothing capacitor C1 needs to be rapidly discharged after the operation of the insulated DCDC converter 2 is stopped. No rapid discharge after shutdown is required.

The voltage detection unit 11 detects the voltage V1 across the smoothing capacitor C1 and outputs it to the control unit 10 . Also, the voltage detection unit 12 detects the voltage V2 across the smoothing capacitor C2 and outputs it to the control unit 10 . Furthermore, the current detection unit 13 detects the inductor current IL flowing through the inductor L and outputs it to the control unit 10 . The control unit 10 controls the switches SW1 and SW2, and based on the detected voltages V1 and V2 and the inductor current IL, generates and outputs gate control signals Sg1 to Sg8 for the switching elements Q1 to Q8. As a result, the insulated DCDC converter 2 is operated as a bi-directional converter during normal operation, and the "preparation process before starting operation" in FIG. 3 is executed before starting operation.

FIG. 3 is a flowchart showing preparatory processing performed by the control unit 10 of FIG. 2 before starting operation.

In step S1 of FIG. 3, a failure diagnosis process is executed. Specifically, the switches SW1 and SW2 are turned off, and the voltage V1 of the smoothing capacitor C1 is charged to the voltage Va required for failure diagnosis. Next, in step S2, an insulation diagnosis process is executed. Specifically, the switches SW1 and SW2 are turned off, and the voltage V1 of the smoothing capacitor C1 is charged to the voltage Vb required for insulation diagnosis. Further, in step S3, voltage adjustment processing before connection with the storage battery 1 is executed. discharge to a voltage below In step S4, a voltage adjustment process is executed before the DCAC inverter device 3 operates. 3 is charged to the voltage Vc required for the operation.

4A is a timing chart of each signal showing an operation example when the inductor current IL is continuous in step-up switching and synchronous rectification is performed in the isolated DCDC converter 2 of FIG. 2. FIG. FIG. 4B is a timing chart of each signal showing an operation example when the inductor current IL is continuous in step-up switching and no synchronous rectification is performed in the isolated DCDC converter 2 of FIG. When the gate control signals Sg1 to Sg8 are 1 (high level), the switching elements Q1 to Q8 are turned on. When the gate control signals Sg1 to Sg8 are 0 (low level), the switching elements Q1 are turned on. .about.Q8 are turned off, and so on.

4A and 4B show the inductor current IL when the switching elements Q1 to Q8 of the switching circuits 7 and 8 are driven by the gate control signals Sg1 to Sg8, respectively. A dead time Tdead is set to prevent current flow. Tφ is a phase shift amount which will be described in detail later. As can be seen from the comparison between FIGS. 4A and 4B, the gate control signals Sg5 to Sg8 differ depending on whether or not synchronous rectification is performed.

FIG. 5A is a timing chart of each signal showing an operation example when the inductor current IL is discontinuous in step-up switching and synchronous rectification is performed in the isolated DCDC converter 2 of FIG. FIG. 5B is a timing chart of each signal showing an operation example when the inductor current IL is discontinuous in step-up switching and there is no synchronous rectification in the isolated DCDC converter 2 of FIG.

5A and 5B show the inductor current IL when the switching elements Q1 to Q8 of the switching circuits 7 and 8 are driven by the gate control signals Sg1 to Sg8, respectively. A dead time Tdead is set to prevent current flow. As can be seen from the comparison between FIGS. 5A and 5B, the gate control signals Sg5 to Sg8 are different depending on the presence or absence of synchronous rectification.

FIG. 6 is a timing chart of the inductor current IL in the insulated DCDC converter 2 of FIG. 2 when the inductor current IL is at the maximum value in step-up switching and the inductor current IL is continuous.

In FIG. 6, currents ΔI1, ΔI2, ΔI3, on-time Ton, Ton2, and off-time Toff are represented by the following equations.

ΔI1=(Vin×Ton)/L
ΔI2=(Vin-Vout)Toff/L
ΔI3=-(Vin+Vout)・Ton2/L
Ton=Tφ-Ton2
Ton2
= {−(Toff·Vout)+(Tφ+Toff)·Vin}
/(Vout+2.Vin)
Toff=T/2-Tφ

where Vin is the input voltage, Vout is the output voltage, and L is the inductance of inductor L.

FIG. 7 is a timing chart of the inductor current IL when the inductor current IL is discontinuous and the inductor current IL has a maximum value in step-up switching in the isolated DCDC converter 2 of FIG.

In FIG. 7, current ΔI1, ON time Ton, and OFF time Toff1 are represented by the following equations. Although the theoretical formula for the maximum current value differs depending on whether the inductor current IL is continuous or discontinuous, the theoretical formula for current discontinuity is used as a guideline for the maximum current value for simplifying calculations.

ΔI1 = (Vin·Ton)/L
Ton=Tφ-Tdead
Toff1=(Vin·Ton)/(Vout−Vin)

FIG. 8A is a timing chart of each signal showing an operation example when the inductor current IL is continuous in step-down switching and synchronous rectification is performed in the isolated DCDC converter 2 of FIG. FIG. 8B is a timing chart of each signal showing an operation example when the inductor current IL is continuous in step-down switching and without synchronous rectification in the isolated DCDC converter 2 of FIG.

8A and 8B show the inductor current IL when the switching elements Q1 to Q8 of the switching circuits 7 and 8 are driven by the gate control signals Sg1 to Sg8, respectively. A dead time Tdead is set to prevent current flow. Tφ is a phase shift amount which will be described in detail later. As can be seen from the comparison between FIGS. 8A and 8B, the gate control signals Sg5 to Sg8 differ depending on whether or not synchronous rectification is performed.

FIG. 9A is a timing chart of each signal showing an operation example when the inductor current IL is discontinuous in step-down switching and synchronous rectification is performed in the isolated DCDC converter 2 of FIG. FIG. 9B is a timing chart of each signal showing an operation example when the inductor current IL is discontinuous in step-down switching and there is no synchronous rectification in the isolated DCDC converter 2 of FIG.

9A and 9B show the inductor current IL when the switching elements Q1 to Q8 of the switching circuits 7 and 8 are driven by the gate control signals Sg1 to Sg8, respectively. A dead time Tdead is set to prevent current flow. As can be seen from the comparison between FIGS. 9A and 9B, the gate control signals Sg5 to Sg8 differ depending on whether or not synchronous rectification is performed.

FIG. 10 is a timing chart of the inductor current IL in the insulated DCDC converter 2 of FIG. 2 when the inductor current IL is at the maximum value in step-down switching and the inductor current IL is continuous.

In FIG. 10, currents ΔI1, ΔI2, ΔI3, ON times Ton, Ton2, and OFF times Toff are represented by the following equations.

ΔI1=(Vin−Vout)・Ton/L
ΔI2=−(Vout・Toff)/L
ΔI3=-(Vin+Vout)・Ton2/L
Ton=Tφ-Ton2
Ton2
= {−(Vout·T)+(2·Tφ·Vin)}/(4·Vin)
Toff=T/2-Tφ

FIG. 11 is a timing chart of the inductor current IL when the inductor current IL is at its maximum value in step-down switching and is discontinuous in the isolated DCDC converter 2 of FIG.

In FIG. 11, current ΔI1, on-time Ton, and off-time Toff1 are represented by the following equations. Although the theoretical formula for the maximum current value differs depending on whether the inductor current IL is continuous or discontinuous, the theoretical formula for current discontinuity is used as a guideline for the maximum current value for simplifying calculations.

ΔI1=(Vin−Vout)・Ton/L
Ton=Tφ-Tdead
Toff1=(Vin−Vout)·Ton/Vout

FIG. 12 is a flow chart showing a pre-charging control process (outline control flow) executed by the control unit 10 of FIG.

Here, the phase shift amount Tφ in the step-down mode is expressed by the following equation.

Tφ=Ton+T dead
Ton = (IL target L) / (Vin-Vout)

Here, ILtarget is the target current value flowing through the inductor L.

Also, the phase shift amount Tφ in the boost mode is expressed by the following equation.

Tφ=Ton+T dead
Ton=(IL target L)/Vin

In step S11 of the pre-charging process (outline flow) of FIG. 12, the switching unit 9 is operated with the minimum phase shift amount Tφmin in the step-down mode. Next, in step S12, the switching unit 9 is step-down switched with a phase shift amount Tφ (Tφ calculated as ILtarget=ILmax) at which the inductor current IL reaches the maximum value ILmax according to the voltage difference between the input voltage Vin and the output voltage Vout. buck mode). Then, in step S13, it is determined whether or not the voltage of the smoothing capacitor (in the case of C1 discharge of 150 V, the voltage of the input capacitor, and in the case of C1 discharge of 150 V, the voltage of the output capacitor) is within the target value setting range, When the answer is YES, the pre-charging process is terminated, and when the answer is NO, the process proceeds to step S14. In step S14, it is determined whether or not the switching unit 9 is operating in step-down switching (step-down mode). If YES, the process proceeds to step S15. If NO, the process proceeds to step S16. In step S15, it is determined whether or not the calculation result Tφ<Tφmax (the upper limit of the phase shift amount Tφ) at which the inductor current IL reaches the maximum value ILmax. , NO, the process proceeds to step S16. In step S16, the switching unit 9 is operated in step-up switching (step-up mode) with a phase shift amount Tφ at which the inductor current IL becomes the maximum value ILmax according to the input voltage Vin.

In the pre-charging process of FIG. 12, the following processes are omitted from the actual operation process.
(1) Soft-start processing in which the current gradually increases.
(2) Charge standby processing for waiting at the minimum output (zero) so that recharging can be started immediately when the voltage changes by a predetermined amount or more after charging is completed.

The pre-charging control process configured as described above can be used in each of the processes S1 to S4 in the preparatory process before starting operation in FIG. The switching unit 9 is operated in step-down switching (step-down mode) with a phase shift amount Tφ at which the inductor current IL becomes the maximum value ILmax (S11) until the input capacitor voltage) reaches the target voltage range (S11). If Tφ<Tφmax (YES in step S14) during operation in switching (step-down mode) (YES in step S15), in step S12, the switching unit 9 is switched to the inductor current according to the voltage difference between the input voltage Vin and the output voltage Vout. Operation is performed in step-down switching (step-down mode) with a phase shift amount Tφ at which IL is the maximum value ILmax. On the other hand, if the switching unit 9 is not operating in step-down switching (step-down mode) (NO in step S14) or is operating in step-down switching (step-down mode) (YES in step S14), Tφ≧Tφmax. If (NO in S15), in step S16, the switching unit 9 is operated in boost switching (boost mode) with a phase shift amount Tφ at which the inductor current IL becomes the maximum value ILmax according to the input voltage Vin.

FIG. 13 is a diagram showing a table of charge/discharge control modes executed by the switching section 9 of FIG. As is clear from FIG. 13, the isolated DCDC converter 2 has the following four control modes. Note that the voltage is an example during operation.
(1) C1 charging 150 V: The input voltage Vin becomes the voltage V2, the output voltage Vout becomes the voltage V1, the switches SW1 and SW2 are turned off, the operation is performed in a state in which the storage battery 1 is disconnected, and the smoothing capacitor C1 is charged. Operation mode.
(2) C1 charging 450V: The input voltage Vin becomes the voltage V2, the output voltage Vout becomes the voltage V1, the switches SW1 and SW2 are turned off, the operation is performed in a state in which the storage battery 1 is disconnected, and the smoothing capacitor C1 is charged. Operation mode.
(3) C1 discharge 150 V: The input voltage Vin becomes the voltage V1, the output voltage Vout becomes the voltage V2, the switches SW1 and SW2 are turned off, the operation is performed in a state in which the storage battery 1 is disconnected, and the smoothing capacitor C1 discharges. Operation mode.
(4) C2 charging 280 V: The input voltage Vin becomes the voltage V1, the output voltage Vout becomes the voltage V2, the switches SW1 and SW2 are turned on, the operation is performed in the state where the storage battery 1 is connected, and DC power is discharged from the storage battery 1. This is the operating mode for

13 is the process of step S31 in FIG. 14B. 13 is one step of processing in step S32 of FIG. 14B. The reason why there is an item for charge/discharge in FIG. 13 is that the timing chart differs between charge and discharge. The above-described FIGS. 4A, 4B, 5A, 5B, 8A, 8B, 9A, and 9B are patterns during discharging, in which the primary side and secondary side are switched during charging, and the gate control signal during discharging Sg1, Sg2, Sg3, Sg4, Sg5, Sg6, Sg7 and Sg8 become gate control signals Sg5, Sg6, Sg7, Sg8, Sg1, Sg2, Sg3 and Sg4 during charging, respectively. That is, the corresponding gate control signal Sg in the timing chart differs between charging and discharging.

14A to 14C are flow charts showing the pre-charging control process (detailed control flow) executed by the control unit 10 of FIG. 14A to 14C, an operation example of "C1 charging 150V" of the operation modes of FIG. 13 will be described below. In this operation example, the smoothing capacitor is C1 and its output voltage is V1. As is clear from FIG. 13, in C1 discharge or C2 charge, the smoothing capacitor is C2 and its output voltage is V2.

In step S21 of FIG. 14A, first, an initial setting process is performed. Specifically, the control mode is set to C1 charge 150V, the parameters Bb and Bbnext are set to "step down", and the charge/discharge mode is set to "charge". Also, the input voltage Vin is set to the C2 voltage (V2), the output voltage Vout is set to the C1 voltage (V1), and the current target value ILtarget is set to a predetermined current start value ILstart.

Next, in step S22, it is determined whether or not the parameter Bb is "lower pressure". If YES, the process proceeds to step S23. If NO, the process proceeds to step S41 in FIG. 14C. In step S23, Tφ step-down upper limit determination processing is executed. Specifically, it is determined whether or not Vin−Vout<ILtarget×L/(Tφmax−Tdead). If NO, go to step S24. Here, Tφmax is the maximum value of the phase shift amount Tφ.

In step S24, the phase shift amount Tφ is set to the step-down calculated value. Specifically, the ON time Ton is set to ILtarget×L/(Vin−Vout), and the phase shift amount Tφ is set to Ton+Tdead. Next, in step S25, the current target value ILtarget is updated. Specifically, the target value ILtarget of the inductor current IL is set to ILtarget+ILstep. However, when ILtarget>ILmax (the upper limit value of the inductor current IL), the target value ILtarget of the inductor current IL is set to ILmax. Then, in step S26, the parameter Bbnext is set to "step down", and the process proceeds to step S29 in FIG. 14B.

In step S27, the phase shift amount Tφ is set to the step-down upper limit value Tmaxbu, and in step S28, the parameter Bbnext is set to "boost", and then the process proceeds to step S29 in FIG. 14B.

In step S29 of FIG. 14B, a PWM signal including the gate control signals Sg1 to Sg8 is generated with the set phase shift amount Tφ and output to the switching section 9, thereby driving the switching section 9 to operate. Next, in step S30, the parameter Bb is set to the data of the parameter Bbnext, and in step S31, a voltage target value upper limit reach determination process is executed. Specifically, it is determined whether or not V1≧V1max. If YES, the process proceeds to step S32. If NO, the process returns to step S22 in FIG. 14A. In step S32, a charge waiting process for the capacitor is executed. Specifically, after the capacitor voltage of the output voltage Vout (the voltage V1 at C1 charging 150V) is within the target voltage range and the switching unit 90 is controlled to operate with the minimum phase shift amount Tφ (output current zero) , the process returns to step S22 of FIG. 14A.

In step S41 of FIG. 14C, an input/output voltage difference upper limit determination process is executed. Specifically, it is determined whether or not Vin−Vout>(ILmax+ILmargin)×L/(Tφmax−Tdead). If YES, the process proceeds to step S42. If NO, the process proceeds to step S43. Here, ILmargin is a predetermined margin value of inductor current IL. Next, in step S42, after stopping the output of the PWM signal for a predetermined period, the process returns to step S21 in FIG. 14A.

In step S43, the phase shift amount Tφ is set to the boost calculated value. Specifically, the ON period Ton is set to ILtarget×L/Vin, and the phase shift amount Tφ is set to Ton+Tdead. Next, in step S44, a boost upper limit determination process for the phase shift amount Tφ is executed. Specifically, it is determined whether or not Tφ>Tφmaxbo. The process proceeds to step S45. Here, Tφmaxbo is the boost upper limit value of the phase shift amount Tφ. In step S45, the current target value ILtarget is updated. Specifically, ILtarget is incremented by a predetermined step value ILstep, and when ILtarget>ILmax, ILtarget is set to the inductor current maximum value ILmax. In step S46, the phase shift amount Tφ is set to the boost upper limit value Tφmaxbo, and then the process returns to step S29.

The pre-charging control process configured as described above can be used in each of the processes S1 to S4 in the preparatory process before starting operation in FIG. , until the output voltage of the smoothing capacitor reaches the target voltage range, the switching unit 9 is operated with the phase shift amount Tφ such that the inductor current IL becomes the upper limit value, and the output voltage of the smoothing capacitor reaches the upper limit value of the target voltage range. If so, the charging control process of the smoothing capacitor in step S32 is executed. In the smoothing capacitor charging control process, the output voltage of the smoothing capacitor is within the target voltage range, the switching unit 9 is operated with the minimum phase shift amount Tφ (output current is zero), and in this state the output voltage of the smoothing capacitor reaches the target voltage. When the lower limit of the voltage range is reached, the process returns to the smoothing capacitor charging process.

FIG. 15 is a simulation result of the insulated DCDC converter 2 of FIG. 2 and is a timing chart of each signal. For the convenience of simulation, the inventors performed verification using two-phase interleaving.

As is clear from the phase shift amounts φ1 and φ2 in FIGS. 15A and 15B, the phase shift amount Tφ gradually increases, switches to step-up when reaching the step-down upper limit, and gradually increases from the step-up lower limit. I understand. Also, the voltage V2 in FIG. 15(c) stops when it reaches the target value. Furthermore, the inductor currents IL1 and IL2 in FIGS. 15(d) and (e) are different from each other by 90 degrees, and the current gradually increases. become zero. FIG. 15(f) shows the step-up/step-down flag BFF, where BFF=0 indicates step-down and BFF=1 indicates step-up.

By monitoring the inductor current value detected by the current detection unit 13 and determining the current upper limit value, the control unit 10 can flow the inductor current IL up to the limit of the current upper limit value, thereby enabling more rapid discharge. .

As described above, according to the present embodiment, by executing the pre-charging control process shown in FIG. 12 or FIGS. Based on the output voltage, the switching unit 9 is controlled to adjust the input voltage and the output voltage so that the inductor current IL flowing through the inductor L is less than a predetermined upper limit value. Therefore, in the isolated DCDC converter, the voltage of the smoothing capacitor can be controlled in a relatively short period of time within a predetermined operating time with a simpler configuration than in the prior art.

(Modification)
FIG. 16 is a block diagram showing a configuration example of a power conversion system according to a modification. The power conversion system according to the modification of FIG. 16 differs from the power conversion system of FIG. 1 in the following points.
(1) A solar cell 5 and a DCDC converter 6 are further provided. Here, the output terminal of the DCDC conversion device 6 is connected in parallel to the connection point between the isolated DCDC conversion device 2 and the DCAC inverter device 3 .
Differences will be described below.

In FIG. 16, the DC voltage associated with the DC power generated by the solar cell 5 is converted to a predetermined DC voltage by the DCDC converter 6, and then charged to the storage battery 1 via the insulated DCDC converter 2, or the DCAC It is output to the load 4 via the inverter device 3 .

In the power conversion system according to the modification configured as described above, the DC power generated by the solar cell 5 can be charged to the storage battery 1 or output to the load 4 . Moreover, since the power conversion system according to the modification includes the insulated DCDC converter 2, it has the same effects as the power conversion system according to the embodiment.

As described in detail above, according to the isolated DCDC converter of the present invention, the inductor current flowing through the inductor becomes less than the predetermined upper limit based on the input voltage and the output voltage in the preparatory operation before starting operation. The switching section is controlled so as to regulate the input voltage and the output voltage. Therefore, in the isolated DCDC converter, the voltage of the smoothing capacitor can be controlled in a relatively short period of time within a predetermined operating time with a simpler configuration than in the prior art.

1 Storage Battery 2 Insulated DCDC Converter 3 DCAC Inverter 4 Power System (or Load)
5 Solar cell 6 DCDC converters 7, 8 Switching circuit 9 Switching unit 10 Control units 11, 12 Voltage detection unit 13 Current detection unit C1, C2 Smoothing capacitors D1 to D8 Reverse conducting diode L Inductor L1 Primary winding L2 Secondary winding Lines Q1 to Q8 Switching elements SW1 and SW2 Switches T11 to T14 Terminal TR Insulating transformer

Claims (6)

a first smoothing unit including a first capacitor for smoothing an input voltage;
A switching unit composed of an insulating transformer, an inductor, a switching circuit on the primary side of the insulating transformer, and a switching circuit on the secondary side of the insulating transformer, and switches the smoothed voltage. a switching unit that converts power to a predetermined output voltage;
a second smoothing unit including a second capacitor for smoothing the power-converted output voltage;
An insulated DCDC converter comprising a control unit that controls a preparatory operation before starting operation of the switching unit,
The control unit adjusts the input voltage and the output voltage based on the input voltage and the output voltage in a preparatory operation before starting operation so that an inductor current flowing through the inductor is less than a predetermined upper limit value. controlling the switching unit to
Insulated DCDC converter. The preparatory operation before starting operation includes:
(1) failure diagnosis processing for charging the output voltage to a voltage required for failure diagnosis;
(2) insulation diagnosis processing for charging the output voltage to a voltage required for insulation diagnosis;
(3) a voltage adjustment process of charging the output voltage to the rated voltage of the storage battery, which is a process before connecting the first smoothing unit to the storage battery;
(4) voltage adjustment processing for charging the output voltage to a voltage required for operation of the switching unit;
is either
The isolated DCDC converter according to claim 1. The control unit
(1) Operate the switching unit by step-down switching with a phase shift amount such that the inductor current becomes a predetermined upper limit until the output voltage reaches the target voltage range, and the output voltage is less than the upper limit. For example, the switching unit is operated by step-down switching,
(2) operating the switching unit with step-up switching when the switching unit is not operating with step-down switching, or when the output voltage is not less than the upper limit value even if the switching unit is operating with step-down switching;
to control,
3. The insulated DCDC converter according to claim 1 or 2. an isolated DCDC converter according to any one of claims 1 to 3;
A power conversion system comprising: a DCAC inverter device that converts an output voltage output from the insulated DCDC conversion device into an AC voltage. The power conversion system according to claim 4,
The power conversion system is
A power conversion system, further comprising a DCDC conversion device that converts an input voltage output from a solar cell into a predetermined output voltage and outputs the output voltage to the insulated DCDC conversion device or the DCAC inverter device. a first smoothing unit including a first capacitor for smoothing an input voltage;
A switching unit composed of an insulating transformer, an inductor, a switching circuit on the primary side of the insulating transformer, and a switching circuit on the secondary side of the insulating transformer, and switches the smoothed voltage. a switching unit that converts power to a predetermined output voltage;
a second smoothing unit including a second capacitor for smoothing the power-converted output voltage;
A control method for an insulated DCDC converter comprising a control unit for controlling a preparatory operation before starting operation of the switching unit,
The control unit adjusts the input voltage and the output voltage based on the input voltage and the output voltage in a preparatory operation before starting operation so that an inductor current flowing through the inductor is less than a predetermined upper limit value. controlling the switching unit to
A control method for an insulated DCDC converter.

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